Conventional pumps and other devices often include a drive shaft which extends into a housing through an orifice in the housing for rotating elements within the housing, and a drive shaft seal for preventing fluid from escaping from within the housing through the orifice. One type of drive shaft seal includes a rotating sealing ring fixedly connected to the drive shaft in the orifice and a stationary sealing ring fixedly connected to the housing in the orifice. A surface of the rotating ring is pressed against a mating surface of the stationary ring, for example by a spring, so as to prevent fluid from flowing between the rings as the rotating ring rotates relative to the stationary ring.
When the drive shaft rotates, friction between the rings results in generation of heat. Under normal operating conditions, when a thermally conductive fluid is present within the housing, heat typically flows from one of the rings into the fluid so as to cool the rings. This occurs in conventional pumps of the type including a drive shaft which rotates an impeller immersed in a fluid, and in which the fluid is in contact with one of the sealing rings.
However, when highly thermally conductive fluid (such as water) within the housing is replaced by fluid having lower thermal conductivity (such as air), less heat is dissipated away from the sealing rings. High sealing ring temperatures may result, and may cause damage to the seal, housing, or other components within the housing. A fluid leak is a likely consequence.
Use of a heat dissipating means to mitigate this problem has been proposed, for example, in U.S. Pat. No. 3,826,589, issued July 30, 1974 to Frank, et al. U.S. Pat. No. 3,826,589 discloses a pump having a plastic housing, and a drive shaft extending into the interior of the housing. Carbon insert 37, which is attached to (and rotates with) the drive shaft, is pressed against and rotates relative to stationary ceramic insert 40. Insert 40 presses against stationary sealing ring 41. Sealing ring 41 in turn presses thermally conductive, frustoconical shield 43 against the housing. The shield is shaped so that even when the water level within the pump falls to a low level, a portion of the shield is immersed in the water. Thus, heat is conducted from inserts 37 and 40 through ring 41 and shield 43 to the water.
However, if the water level within the pump of U.S. Pat. No. 3,826,589 were to fall so far that shield 43 were no longer immersed in the water, the U.S. Pat. No. 3,826,589 system would not efficiently dissipate heat away from the drive shaft seal (i.e., from inserts 37 and 40). Further, the design of the U.S. Pat. No. 3,826,589 pump has the disadvantage that the heat dissipating shield contacts the fluid within the pump, so that fluid flow within the pump is affected by the shield and the shield is subject to corrosion and other undesirable effects due to exposure to the fluid.
A more complicated heat dissipation means is disclosed in U.S. Pat. No. 4,114,899, issued Sept. 19, 1978 to Kulzer, et al. The mechanical seal of U.S. Pat. No. 4,114,899 includes ring 19 (connected to drive shaft 4) which rotates relative to ring 20 (connected to housing 23). The seal is cooled, not only by fluid supplied from fluid volume B contained within the housing, but by conduction of heat from ring 20 through housing sections 23a, 23b, and 23c to the atmosphere surrounding the housing. In one embodiment, the outer surface of housing 23 has ribs 35a, 35b, and 35c extending therefrom. In another embodiment (described with reference to FIG. 2 of U.S. Pat. No. 4,114,899), the outer surface of the housing has a recess (35d) into which fan 50 blows air to assist in heat transfer from the housing's outer surface to the surrounding atmosphere.
However, the seal disclosed in U.S. Pat. No. 4,114,899 is undesirably complicated, and would not facilitate efficient heat transfer to the surrounding atmosphere unless the housing consists of material with high thermal conductivity. This decreases design flexibility by preventing use of other housing materials which happen to have low thermal conductivity, though their other properties may be desirable for intended system applications. Further, the configuration of the U.S. Pat. No. 4,114,899 system, including the shape of the housing's external surface in the U.S. Pat. No. 4,114,599 system, is not optimal for dissipating heat from the drive shaft seal to the surrounding atmosphere.
It has not been known until the present invention how to design a drive shaft seal in a manner eliminating the deficiencies and disadvantages of conventional drive shaft seals such as those described above.